The present invention relates to the medical arts. It particularly relates to the measurement of a diagnostic glucose level in a human subject, especially for the monitoring of diabetic patients, and will be described with particular reference thereto. However, the invention will also find application in conjunction with the non-invasive measurement of concentrations of other proteins and other optically active substances in the human body for medical diagnosis and monitoring. For example, the invention is contemplated to be applied for measuring xcex2-amyloid protein concentrations in the body, which are indicative of Alzheimer""s disease.
Diabetes is presently the fourth leading cause of mortality in the United States. Diabetes can lead to severe complications over time, including blindness, renal and cardiovascular diseases, and peripheral neuropathy associated with limbs. Diabetics typically exhibit poor blood circulation in lower extremities of the body which can lead to gangrene and subsequent amputation.
These and other diabetic complications can typically be minimized or avoided by suitable medical intervention. In the case of diabetes mellitus which relates to inadequate insulin production by the body, a regular administration of insulin injections helps convert glucose to glycogen to control diabetic symptoms and complications. The insulin-injection therapy is preferably closely monitored by frequently measuring diagnostic glucose levels. In a usual approach, blood is drawn and the serum glucose level is measured. Since this monitoring should be done regularly, e.g. on a daily basis, it is preferably self-administered, typically using a finger-prick blood extraction.
A problem arises because diabetic patients are reluctant to perform regular glucose monitoring by painful blood extraction. Blood extraction can also produce infections or introduce harmful contaminants into the body. For these and other reasons, patients sometimes neglect the invasive glucose self-monitoring and fail to adjust their insulin intake to accommodate changes and variations in glucose level. Hence, there is a continuing need for an improved and preferably non-invasive glucose monitoring method and apparatus which conveniently measures a diagnostic glucose level in the human body.
A number of approaches have been developed for determining the glucose level in ocular tissue. In particular, the glucose concentration in the aqueous humor of the eye closely mimics glucose levels in the blood. Furthermore, glucose is an optically active material whose concentration in an aqueous solution can be measured by optical polarimetric methods.
U.S. Pat. No. 5,209,231 issued to Cote et al., U.S. Pat. No. 5,560,356 issued to Peyman, and U.S. Pat. No. 6,370,407 issued to Kroeger et al. are exemplary of recent efforts to exploit the optical activity of glucose in the aqueous humor to monitor a diagnostic glucose level. However, there remains a need in the art for an improved non-invasive diagnostic glucose monitoring which is convenient for diabetic patients to use, does not require ocular implants or refractive index-matching material, provides automatic corrections for individual variations in ocular geometry and optical properties, and is optically robust and substantially insensitive to minor deviations from the designed optical alignment or configuration.
The present invention contemplates an improved apparatus and method which overcomes the aforementioned limitations and others.
According to one aspect of the invention, a method is provided for determining a diagnostic glucose level for a person. Light is reflected off an ocular lens at a Brewster""s angle. A polarization rotation of the reflected light is measured after exiting the eye. A glucose concentration is determined based on the measured polarization rotation.
According to another aspect of the invention, a method is provided for determining a diagnostic glucose level. Light is reflected from an internal ocular interface at an incident angle that has a selected reflection polarization characteristic. A polarimetric parameter of the reflected light is measured. A glucose concentration is computed based on the polarimetric parameter.
According to yet another aspect of the invention, an apparatus is disclosed for determining a diagnostic glucose level in a human subject. A light source produces collimated light at a selected wavelength. The collimated light is arranged such that the collimated light passes through a portion of an eye of the subject and reflects off an eye lens at a selected angle as reflected light. A polarization analyzer measures a polarization of the reflected light that exits the eye. A path length processor determines an optical path length of the reflected light within an aqueous humor of the eye. A glucose level processor computes a glucose concentration based on the measured polarization and the determined optical path length.
One advantage of the present invention resides in providing convenient and robust non-invasive monitoring of blood glucose levels for calibrating insulin injections or other medical treatment of the diabetic condition.
Another advantage of the present invention resides in improved accuracy and precision in non-invasive measurement of glucose concentration in the human body.
Yet another advantage of the present invention resides in providing a painless method and apparatus for monitoring glucose levels in diabetic patients.
Numerous additional advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiment.